Water-swelling polymers are also called a water absorptive polymer. The water-swelling polymers are highly water-retentive due to hydrophilicity and closslinked network of the polymer itself, and are used, alone or in combination with other resins, in various fields that require hydrophilicity such as water permeability, moisture permeability, as well as water retentivity, water swelling property, antistatic characteristics, etc.
Meanwhile, there has been a demand for reduction of organic solvent use in view of its toxicity and air polluting characteristics, and therefore various investigations have been conducted in the field of various resins to make a transition from organic solvent-based resins which are prepared as a solution of the resins in an organic solvent, to aqueous resins which are prepared as an aqueous dispersion of the resins.
Thus, there has been a demand for a water-swelling polymer that can be blended easily in an aqueous resin and is capable of providing excellent hydrophilicity. For example, there has been proposed in Patent Document 1 (see below) that a polyurethane resin obtained by reaction of a urethane prepolymer having an anionic group with a polyoxyethylene group-containing polyamine has excellent compatibility with aqueous resins and is capable of providing excellent hydrophilicity.
Also, there has been known that a moisture-permeation and water-proof treatment is given to fibers in order to block rainwater but allow moisture (water vapor) such as sweat to pass through.
With respect to a coating agent for such a moisture-permeation and water-proof treatment, various investigations have been conducted to make a transition from organic solvent-based resins to aqueous resins.
For example, there has been proposed an aqueous polyurethane resin in which a polyurethane resin containing a hydrophobic macropolyol and a polyurethane resin containing a hydrophilic macropolyol with 50 wt % or more of a polyoxyethylene group are partially and chemically bonded through a chain extender (for example, see Patent Document 2 below).
Further, there has been proposed an aqueous polyurethane resin in which a polyurethane resin is dispersed or dissolved in water: the polyurethane resin being obtained by reaction of a hydrophobic macropolyol made of a polyoxyalkylenepolyol having an alkylene group with 3 to carbons and/or a polyester polyol; a polyisocyanate containing at least 4,4′-methylenebis(cyclohexyl isocyanate); a nonionic inner emulsifier containing two or more active hydrogen groups or two or more isocyanate groups, and having a polyoxyethylene group in its side chain; and a chain extender containing at least polyamine (see, for example, Patent Document 3 below).    Patent Document 1: Japanese Unexamined Patent Publication No. 2005-060690    Patent Document 2: International Patent Publication No. WO2006/062165 A1    Patent Document 3: Japanese Unexamined Patent Publication No. 2006-335950